This application proposes interdisciplinary research on the regulation and function of the high-affinity choline transporter (CHT). The CHT imports choline for the synthesis of acetylcholine (ACh) into cholinergic neurons and thereby controls the capacity of cholinergic neurons to sustain increases in cholinergic neurotransmission. Choline uptake is primarily regulated by the density of CHTs in synaptosomal plasma membrane. The rates of CHT internalization and outward trafficking determine the density of CHTs in plasma membrane. Accumulating evidence indicates that these intracellular CHT transport mechanisms are highly regulated by diverse signaling pathways. This research will test the general hypothesis that CHT capacity limitations constrain the ability of cholinergic neurons to mediate heightened demands on cognitive activity, specifically motivated, attentional performance under challenging conditions. We will study mice expressing a reduced level of CHTs and exhibiting an attenuated capacity of cholinergic neurons to sustain increases in ACh release, intact rats following the blockade of CHT-mediated choline uptake in prefrontal cortex, and humans heterozygous for a variant of the CHT that reduces choline transport capacity by 40-50%. This research will employ molecular, neurochemical, neuropsychological and neuroimaging techniques in order to determine the cellular and neuronal mechanisms that limit CHT capacity in situations that tax cholinergic functions and thereby limit cognitive capacity. Results are expected to demonstrate that a reduced capacity for CHT-mediated choline uptake robustly attenuates the recover of attentional performance after performance challenges, and that such impaired performance is mediated via insufficient levels of prefrontal cholinergic neurotransmission (rodents) and insufficient activation of right prefrontal cortex (humans). Collectively, this research will determine the neuronal mechanisms that constrain behavioral and cognitive capacities, reveal neuronal mechanisms that contribute to cognitive decline, and define new targets for the development of preventive and symptomatic treatments for the cognitive symptoms of neuropsychiatric and neurodegenerative disorders. PUBLIC HEALTH RELEVANCE: The abnormal regulation of the cortical cholinergic input system plays a major role in the manifestation of the cognitive impairments of neuropsychiatric and neurodegenerative disorders, specifically schizophrenia, dementia and other age-related cognitive impairments. The high-affinity choline transporter strongly influences the capacity of this neuronal system to sustain elevated levels of activity. This research will utilize a wide range of experimental approaches and conduct research in mice, rats, and humans to determine how the choline transporter is regulated and how this transporter limits cognitive capacity. The results from this research are of direct significance for hypotheses concerning the role of this major neuromodulator system in cognitive disorders and for the development of new treatments for such disorders.